It or they will happen.
The word imminence is related to any subject in a possible future of events to come. These events can be spontanious or over time but they will become, and therefore become Imminence. It is closely related to the word imminent which explains the actual event where Imminence explains the event entirely as a whole. Non-Indigenous become Imminence as they will happen but the time frame is not specified.
by The Tenth Doctor March 08, 2009